1. Field of the Invention
The present invention relates to a lithographic apparatus and a device manufacturing method.
2. Related Art
A lithographic apparatus is a machine that applies a desired pattern onto a target portion of a substrate. The lithographic apparatus can be used, for example, in the manufacture of integrated circuits (ICs), flat panel displays, and other devices involving fine structures. In a conventional lithographic apparatus, a patterning means, which is alternatively referred to as a mask or a reticle, can be used to generate a circuit pattern corresponding to an individual layer of the IC (or other device), and this pattern can be imaged onto a target portion (e.g., comprising part of one or several dies) on a substrate (e.g., a silicon wafer or glass plate) that has a layer of radiation-sensitive material (e.g., resist). Instead of a mask, the patterning means can comprise an array of individually controllable elements that generate the circuit pattern.
In general, a single substrate will contain a network of adjacent target portions that are successively exposed. Known lithographic apparatus include steppers, in which each target portion is irradiated by exposing an entire pattern onto the target portion in one go, and scanners, in which each target portion is irradiated by scanning the pattern through the beam in a given direction (the “scanning” direction), while synchronously scanning the substrate parallel or anti-parallel to this direction.
Many scanners employ a movable chuck for supporting the substrate that passes through the patterned beam. The chuck transports the substrate from a loader to an exposure location, and passes the transport beneath the scanning apparatus. In machines of this type, it is vital that the substrate is correctly aligned with the scanning apparatus before exposure begins. Alignment, preconditioning, and measurement of the substrate consumes a significant amount of time compared to the time taken to expose the substrate. A substrate will spend approximately one third (33%) of its total time in a typical machine in metrology (e.g., measuring) and internal handling and transport, and two thirds (67%) of its time being exposed. This represents a considerable inefficiency in the operation of the machine.
Lithography machines, in particular Integrated Circuit (IC) and Flat Panel Display (FPD) machines in which the projection systems are most expensive components of the machine, suffer particularly from this problem. If these components are idle for 33% of the time, this represents a significant waste of the capacity of the machine. FPD substrates are generally very large (e.g., typically 2-3 m along each side), and accordingly the machines required to expose such substrates have a very large footprint.
Therefore, what is needed is a method and apparatus that maximize an exposure time of substrates in a lithographic apparatus and/or to minimize an increase in footprint of the lithographic apparatus when large substrates are exposed.